[yaml2obj] - Set a default value for `PAddr` property of a program header to a value of `VAddr`

`PAddr` corresponds to `p_paddr` of a program header, which is the segment's physical
address for systems in which physical addressing is relevant. `p_paddr` is often equal
to `p_vaddr`, which is the virtual address of a segment.

This patch changes the default for `PAddr` from 0 to a value of `VAddr`.

Differential revision: https://reviews.llvm.org/D76131